In The News

Tracks from Emerald Ash Borers larvae can be seen in an ash tree in Wisconsin. AP (Photo: John Ehlke)

Notice a small, D-shaped hole in your ash tree this year? How about excessive woodpecker damage? Both of these are signs of emerald ash borer activity, and thanks to the arrival of this insect, it’s time to take a hard look at the trees in your yard. This summer, scientists confirmed the insect’s presence in Delaware after it appeared in bug traps used to monitor insect populations. The infestation is destroying millions of ash trees and costing municipalities, property owners and land managers, millions of dollars to address the damage.

Emerald ash borer is a small, flying insect native to Asia that arrived in the United States in 2002, likely as a stowaway on wood used in international shipping. Since then, it’s slowly spread across the U.S. and is now present in 25 states and Canada’s eastern provinces.

While only about 2 percent of Delaware’s tree canopy consists of ash tree, most of the ash trees are located in the northern part of the state, and they are a staple in the landscaping of many neighborhoods.

A Bug’s Life
The emerald ash borer’s larvae are the real culprit. While the adult just munches the leaves of the ash tree, it’s when it bores into the bark of the ash tree – hence its name – and lays its eggs that the real trouble begins. When the larvae hatch, they eat the tissue just under the tree bark – called the cambium layer – carving zig-zagging paths up, down, and around the trunk, effectively cutting off the nutrient and water transit system within the tree. These larvae pupate into adult emerald ash borers, and fly to another ash tree to being the process over again.

The adult emerald ash borer, an Asian insect, munches the leaves of the ash tree, but its larvae bore into the bark.(Photo: Courtesy of New York Department of Environmental Conservation)

The insects go after the old and the ill first. Trees that are already weak and failing are particularly susceptible, especially considering the fact that the ash tree has no natural resistance to these insects.

The emerald ash borer travels by flying, but can appear in new areas when it hitch-hikes on firewood hauled by campers from affected areas to places that have not yet seen the insect. It is important to source your firewood from near your campsite – many campsites have firewood for sale locally.

Identifying Ash Trees
Before anything else, the first step to addressing emerald ash borer infestations is to determine if you have any ash trees on your property. In general, these can be identified primarily by their leaves – they have what is called a compound leaf, when many leaflets are joined to a single stem to form the leaf.

In the case of the ash tree, the compound leaf has five to nine leaflets held to the stem in a symmetrical, opposite pattern. Many sophisticated identification guides exist online and at the library, but it may be just as easy to have a tree care specialist pay a visit to your yard to identify trees and help create a management plan.

Delaware’s ash tree populations consist mostly of white ash, green ash and black ash. “Green ash tends to be in lower, wetter areas in this region,” said Nate Shampine said, Mt. Cuba Center’s Natural Lands Manager, “white ash tends to be higher and dryer.” These trees can grow up to 85 feet tall, and take on a yellow to orange hue in the fall.

Ash trees take on a yellow-to-gold color in the fall

So, You Have an Ash Tree
Once you’ve determined you have an ash tree, it’s time to make some tough decisions. Now that the emerald ash borer is here, there’s no ignoring the problem. There are two main paths available to someone coming up with a management plan for ash trees: get the tree treated to shield it against emerald ash borer infestation or let the tree die. This depends entirely on the tree’s value to you, the owner, and whether or not the tree will become a hazard once it dies and is in danger of dropping limbs or collapsing.

“When you remove a tree you’re not only losing the ecological benefits of that tree—the shade, the habitat, the carbon sequestration, the soil benefits,” said Pete Kingshill, an International Society of Arborists-certified local manager with Bartlett Tree Experts in their Wilmington office. “You also lose the economic value of that tree.”

Two examples of ash management techniques are in effect at Mt. Cuba Center: one for the ash trees found in the gardens, and one for those populations in the wide-ranging open space areas.

Shampine has a lot of work to do to manage the thousands of ash trees under his care. His job involves caring for the 500-plus acres of open space protected by Mt. Cuba Center. In some of Mt. Cuba Center’s areas of forest along waterways, up to 70 percent of the trees are ash trees.

“So that we don’t lose those ecosystem services currently provided by the ash, we’re planting red maples, swamp white oaks, silver maples and ash-leaf maple,” Shampine said. “These are other species besides ash which grow in the floodplains, so we’re diversifying the floodplain forest.” When the ash trees in Mt. Cuba Center’s Natural Lands do die off, the young trees will grow to take their place.

Purple traps are covered in an alluring oil and sticky glue to capture emerald ash borer for monitoring purposes. (Photo: Courtesy of U.S. Department of Agriculture)

“For Mt. Cuba Center’s Natural Lands, losing all the ash trees has a significant impact because those floodplain ecosystems are important,” Shampine said. “But because there’s so many trees, we’re not going to spend hundreds of dollars per tree on thousands of trees – it just doesn’t make financial sense.”

But arborists who work in the cultivated landscape of Mt. Cuba Center’s gardens have a different approach: treat select trees. After determining four ash trees of particular value to the gardens – their desirable autumn color, location and good health were all significant factors in the decision to keep these trees – they brought in tree experts to treat the ash trees against emerald ash borer.

“We wanted to keep some ash around in the gardens,” said Scott Kelley, Head Arborist at Mt. Cuba Center. Keeping a diversity of tree species is important to sustaining biodiversity and an ecological landscape.

Treating the trees will cost money. The type of treatment Mt. Cuba Center’s ash trees received is called Systematic Root Flare Injection—it involves drilling into the tree near the base and supplying the treatment directly into the tree’s cambium layer, which the tree takes up by pressure. While this treatment can cost $350-$450 per treatment per tree, a single treatment protects ash trees from emerald ash borer for up to two years.

“It’s highly effective,” Kingshill said. Field treatments for emerald ash borer have increased by about 40 percent over the past year, and continue to grow, according to Kingshill. “Some homeowners who don’t treat their trees will find that they have a $5,000 tree removal fee to address a hazardous dead ash tree near their house.”

This shows the relative size of an Emerald Ash Borer. (Photo: Missouri Department of Conservation)

To Treat, Or Not To Treat?
Both Kelley and Kingshill recommend assessing the tree’s health and personal value.

“You have to determine if the tree’s in really good shape – no die-back, no rust, looks great – and if it’s in a good location, then I would treat it,” Kelley said. “If it’s in the back of your property or if you don’t particularly care for the tree, there’s no need to treat it.”

Kingshill recommends being proactive about determining a management plan for your ash trees by establishing a relationship with an arborist before the damage is evident. He also recommends vetting the professionals who work with your property.

“The company or individual should have compliance with state and local pesticide applicator licenses,” Kingshill said. “All materials should be applied in a safe and professional manner, and they should have commonsense safety concerns.”

Shampine has a recommendation for homeowners and land managers who are managing ash trees: plant more, different trees.

“I wish that people who take down ash would replace them with something else,” Shampine said. “It’s hard, because you can’t predict what the next ash is going to be. What’s best is to plant a diversity of species.”